Etherified phenol-based formaldehyde condensates are well known cross-linking agents, but they have not been very useful in electrocoating because of various problems, and especially because they include traces of the catalysts used in their preparation. These catalysts are water soluble ions, and they contaminate the electrocoating bath, producing all sorts of difficulties. Also, when phenolic resols are etherified to provide water insolubility, they tend to polymerize and lose their desired monomeric form. Moreover, phenolic resins produce coatings which are badly discolored and possess poor corrosion resistance.
Bisphenol-formaldehyde condensates have overcome some of the difficulties in electrocoating, but it is necessary to prepare these in an economical fashion and without introducing the ionic contaminants which have been found to be difficult and expensive to remove entirely.
It is also known to use strong acid ion exchange resins to catalyze reactions which are conventionally catalyzed using dissolved acids. When phenolic resins are reacted with formaldehyde and then reacted with an alcohol to etherify the aldehyde adduct it is usual to employ a basic catalyst in the first stage of the reaction, and then to switch to an acid catalyst in a second stage in order to carry out the desired etherification. It is also known that an acid catalyst can be used in the first stage of the reaction, but this is not normally done because it leads to polymeric products.